Abstract

Nephrops norvegicus, like other lobsters and crayfish, react to threatening stimuli by producing of the tail-flip escape response. This response, which is important in both predator avoidance and capture by trawling, takes the form of repeated flexions and extensions of the abdomen, produced by the deep abdominal flexor and extensor muscles. Much research has been concentrated on both the metabolic and neuronal factors controlling and limiting the tail-flip swimming of decapod Crustacea, but little attention has been focused upon the interactions between these two areas. This study has examined the tail-flip swimming of N.norvegicus in terms of both metabolic and neuronal limitations. Results have indicated that prolonged swimming and its recovery are limited neither by the availability of energy (from direct, stored sources - endogenous muscle ATP; or from indirect sources - by glycolytic production of ATP from D-glucose),nor by alteration of inter- or intra-cellular conditions by the build up of the glycolytic end product L-lactate. However, the part played by phospho-L-arginine (another short-term energy reserve in muscle) in the limitation of tail-flipping has not been unequivocally defined, and the possibility remains that there may be some metabolic influence in determining the endurance and recovery of swimming. Despite the lack of definitive evidence against any metabolic limitation of escape swimming, the results of further experiments suggest that neuronal factors play a major role in the limitation of tail-flipping. These experiments were designed to assess the importance and site of action of neuronal factors, in particular habituation, in swimming. Furthermore, the waning of tail-flipping in response to repeated stimulation appears to represent true habituation. By the use of both histochemical and morphological techniques, the roles of the muscles of the thoraco-abdominal joint in both tail-flipping and postural control have been partially elucidated. These results suggest both bracing and steering functions for the larger muscles of the two groups examined (thoraco-abdominal extensors and abdominal abductors) and postural roles for the smaller muscles. These investigations also identify suitable areas for further research, not least an examination of the innervation and recruitment of these muscle groups during tail-flipping in order to determine unequivocally their bracing and steering functions.